CRC32 as a hash function option?

[michaeleisel]

CRC32 is nice for speed when we can use _mm_crc32_u*. I was curious if benchmarking had been done with a function like the following:

static inline size_t CRCHash(const char *__s, size_t len) {
	uint32_t __h = 5183;
	int curr = len;
	uint64_t *chunks = (uint64_t *)__s;
	while (curr >= 8) {
		__h = (uint32_t)_mm_crc32_u64((uint64_t)__h, *chunks);
		chunks++;
		curr -= 8;
	}
	if (curr >= 4) {
		uint32_t *bits = (uint32_t *)(__s + len - curr);
		__h = _mm_crc32_u32(__h, *bits);
		curr -= 4;
	}
	if (curr >= 2) {
		uint16_t *bits = (uint16_t *)(__s + len - curr);
		__h = _mm_crc32_u16(__h, *bits);
		curr -= 2;
	}
	if (curr >= 1) {
		__h = _mm_crc32_u8(__h, __s[len - 1]);
	}
	return (size_t)__h;
}

[Tessil]

Hi,

No, I didn't benchmark a lot of hash functions as I don't have much time to spend on that. I prefer to keep the default simple FNV-1a for now and use std::hash<std::string_view> when available but you can easily use your own hash function with the library.

Thibaut